As a strain wave gearing device, a cup type strain wave gearing device having a cup-shaped flexible externally toothed gear, and a silk hat type strain wave gearing device having a silk hat-shaped, flexible externally toothed gear are known. In the cup-shaped externally toothed gear, external teeth are formed on the outer peripheral surface portion of a section at the front opening end of the cylindrical body part which is flexible in a non-circular shape, a diaphragm extending inward in the radial direction is formed on the rear opening end, and a disc-like or annular boss is formed on the inner peripheral edge of the diaphragm. The diaphragm and the boss correspond to the bottom portion of the cup shape. The externally toothed gear is fixedly fastened to a member such as a load side member through the boss. In the silk hat-shaped externally toothed gear, external teeth are formed on the outer peripheral surface portion at the front opening end of the cylindrical body portion, a diaphragm extending radially outward is formed at the rear opening end of the cylindrical body, and an annular boss is formed on the outer peripheral edge of the diaphragm. The diaphragm and the boss correspond to the brim portion of the silk hat shape.
In the cup type strain wave gearing device or the silk bat type strain wave gearing device, each contact portion to be lubricated is lubricated by grease filled inside thereof or applied thereon. A strain wave gearing device which is lubricated with grease may not be able to start with a low capacity motor when it is operated in a low temperature environment.
Patent Document 1 proposes a method of heating a strain wave gearing device from the outside in a low temperature environment, for example, at a low temperature of −30° C. to reduce the viscosity of the grease in order to smoothly drive the strain wave gearing device. In the strain wave gearing device disclosed here, component parts thereof are manufactured from a material having high thermal conductivity, a heater is attached to the outer peripheral surface of the internally toothed gear in a surface contact state, so that heat from the heater is transmitted to the whole of the strain wave gearing device. Based on the measurement result of the thermometer disposed in the vicinity of the heater, the temperature of the heater is adjusted, so that the temperature of grease, which is filled between the internally toothed gear and the externally toothed gear or between the wave generator and the externally toothed gear, or is applied on the inner side of the wave generator, is controlled to be kept constant (paragraphs 0008 to 0014 of Patent Document 1).